Recently, there has been considerable interest within the detergent industry for laundry detergents which are "compact" and therefore, have low dosage volumes. To facilitate production of these so called low dosage detergents many attempts have been made to produce high bulk density detergents, for example with a density of 600 g/l or higher. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers.
Generally, there are two primary types of processes by which detergent granules or powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent granules. In the second type of process, the various detergent components are dry mixed after which they are agglomerated with a binder such as a nonionic or anionic surfactant. In both processes, the most important factors which govern the density of the resulting detergent granules are the density, porosity, particle size and surface area of the various starting materials and their respective chemical composition. These parameters, however, can only be varied within a limited range. Thus, a substantial bulk density increase can only be achieved by additional processing steps which lead to densification of the detergent granules.
There have been many attempts in the art for providing processes which increase the density of detergent granules or powders. Particular attention has been given to densification of spray-dried granules by post tower treatment. For example, one attempt involves a batch process in which spray dried or granulated detergent powders containing sodium tripolyphosphate and sodium sulfate are densified and spheronized in a Marumerizer.RTM.. This apparatus comprises a substantially horizontal, toughened, rotatable table positioned within and at the base of a substantially vertical, smooth walled cylinder. This process, however, is essentially a batch process and is therefore less suitable for the large scale production of detergent powders. More recently, other attempts have been made to provide a continuous processes for increasing the density of "post-tower" or spray dried detergent granules. Typically, such processes require a first apparatus which pulverizes or grinds the granules and a second apparatus which increases the density of the pulverized granules by agglomeration. These processes achieve the desired increase in density only by treating or densifying "post tower" or spray dried granules.
However, all of the aforementioned processes are directed primarily for densifying or otherwise processing "spray dried" granules. Currently, the relative amounts and types of materials subjected to spray drying processes in the production of detergent granules has been limited. For example, it has been difficult to attain high levels of surfactant in the resulting detergent composition, a feature which facilitates production of low dosage detergents. To alleviate such problems, the art and the industry have been addressing processes which entail agglomerating detergent compositions. For example, attempts have been made to agglomerate detergent builders by mixing zeolite and/or layered silicates in a mixer to form free flowing agglomerates. Other developments in this area of the art have provided agglomeration processes which ultimately result in fully formulated compact detergent compositions. As existing detergent plants which are fitted for spray-dried detergents are convened to the modem agglomeration process plants, a need has been identified for techniques and processes which can be easily and economically retro-fitted into such existing plants. It would therefore be desirable to have an agglomeration process for making detergent compositions which is more amenable and economical when implementing into existing spray-drying detergent plants.
Accordingly, there remains a need in the an to have an agglomeration process for continuously producing a high density detergent composition which facilitates conversion of existing spray-drying detergent plants to modem-day agglomeration process plants.